1. Field of the Invention
The present invention relates to a driving method and a driving apparatus of a solenoid wherein in actuating the solenoid, a holding voltage is applied after overexciting the solenoid by applying an overexciting voltage, and relates to a driving control apparatus of various solenoids used in a vehicle automatic transmission. It is suitable, for example, in duty controlling a solenoid, after overexciting the solenoid in an initial stage, a current value is held by a chopper drive.
2. Description of the Related Art
In a general duty drive of a solenoid, for example, in order to generate a predetermined current value according to a duty ratio, a rectangular wave voltage is applied only once during a cycle time of a duty control, however, the operation is apt to delay due to a delay in response of a current value generated in the solenoid. For this reason, in the case where the response property is important, it is designed to overexcite the solenoid in an initial stage of a cycle time of the duty control, and thereafter, a holding voltage is applied. Such a driving apparatus of solenoid is known from, for example, Japanese Utility Model Laid Open Publication No. Hei 1-165381. In such a driving apparatus, 1 hydraulic solenoid valve is driven, and it is arranged to decide an overexciting time depending on an oil temperature. An overexciting current during the overexciting time is maintained, for example, at 140%, 170%, or 200% of a lowest operating current at an ordinary temperature. Furthermore, by setting a longer overexciting time at the time of low oil temperature, a smaller overexciting current may be required by the amount of extension of the overexciting time. In other words, in the case of this driving apparatus, a reliable operation of the solenoid can be achieved with small overexciting current by setting the overexciting time to be relatively long at the time of low oil temperature.
On the other hand, in place of the application of the holding voltage mentioned above, there are some driving apparatus wherein the supply voltage is chopping driven. Here, the chopping drive means a driving mode of repeating on and off at a high frequency such as for example, 1 to 2 kHz, and it is also called chopper drive. Specifically, the solenoid is overexcited at an initial stage of a cycle time of the duty control, and thereafter, a current value is held to be equal to or larger than the predetermined current value by the chopping drive. Such a chopping drive control apparatus is described, for example, in Japanese Patent Laid Open Publication Hei No. 3-177669. In this regard, "on" or "ON" represents to excite the solenoid, and "off" or "OFF" represents a non-exciting state. Also, "chopping" and "chopper" means the same meaning.
However, in the prior art driving apparatus, since the overexciting time is determined depending on an oil temperature, and since an overexciting current is supplied during the determined overexciting time irrespective of a rising condition of the overexciting current, even when the overexciting current has early risen to a current value of a minimum extent required to actuate the solenoid, it must wait for the elapse of the overexciting time, and thus, it is diftfcult to set the overexciting time to a required minimum extent. Furthermore, there is a problem that in order to actuate the solenoid reliably, the overexciting time must include a margin, and hence power consumption and the amount of generated heat are caused to increase by the amount of the margin.
Furthermore, in the solenoid drive control apparatus which performs the chopping drive as described above, an on-off period during the chopping drive, that is, a chopping frequency, and the ratio of on time to off time during one chopping cycle are constant. Accordingly, during one cycle or duty control, first, the overexcitation is made ON for a predetermined time, and then, for a duty ON time corresponding to the duty ratio, a chopper ON and a chopper OFF are repeated at each predetermined time at a single high frequency, and thereafter, an OFF state is continued.
However, a value of current supplied actually to the solenoid is affected, for example, by a voltage value of a power supply such as a vehicle-mounted battery, and by a resistance value of the solenoid itself. Moreover, the resistance value of the solenoid itself is sometimes dependent on a so-called individual difference and an operational environmental temperature. Specifically, when the resistance value of the solenoid is constant, the larger the supplied voltage value, the larger becomes the supplied current value to the solenoid, and also when the resistance value of the solenoid is small and when the operational environmental temperature is low, the supplied current value to the solenoid becomes large. In this manner, the larger the supplied current value to the solenoid than the current value corresponding to the duty ratio, the larger becomes the amount of heat generated from the solenoid, and the energy loss becomes large correspondingly. At the same time, a heat shielding structure becomes necessary, and the structure becomes complicated resulting in an increase in cost.